The present invention relates to attenuation circuits, and more particularly to a high performance attenuator configuration that makes use of integrated junction field effect transistors to integrate functions that previously required mechanical switches.
Because of the requirement that one Megohm oscilloscopes have to be able to withstand input voltages up to one Kilovolt while having only microamperes of leakage, electro-mechanical relays are required to switch various attenuator functions. As shown in FIG. 1 current designs have at least four relay contacts in a signal path between an input connector and an FET preamplifier, with some instruments having many more. These relay switches often are responsible for much of the loss of signal fidelity; they represent a large part of the total attenuator cost since they are required to have low capacitance to ground, low inductance and small size; and they represent the least reliable component on many oscilloscopes.
What is desired is a high performance attenuator configuration that reduces the number of relay switches in the signal path to provide higher bandwidth, lower cost and increased reliability.